1. Field of the Invention
This invention relates to a semiconductor apparatus.
2. Background Art
In a vertical semiconductor apparatuses for power electronics applications, a main current path is formed in the vertical direction between a first main electrode and a second main electrode provided respectively on the frontside and backside of a semiconductor layer. Such semiconductor apparatuses have fast switching characteristics and a reverse blocking voltage (breakdown voltage) of several ten to several hundred volts, and are widely used for electric power conversion and control in home electric apparatuses, communication apparatuses, and car-mounted motors. To achieve downsizing, high efficiency, and low power consumption in these fields, the on-state resistance needs to be reduced. That is, vertical power semiconductor apparatuses are strongly required to have low on-resistance while retaining high breakdown voltage.
The on-resistance of a vertical semiconductor apparatus greatly depends on the electric resistance of its drift layer. The impurity concentration that determines the electric resistance of the drift layer cannot exceed a maximum limit, which depends on the breakdown voltage of the pn junction formed between the base region and the drift layer. Thus, there is a tradeoff between the device breakdown voltage and the on-resistance. Improving this tradeoff is important for low power consumption devices. This tradeoff has a limit determined by the device material.
The so-called superjunction structure is known as a structure to solve this problem. In the superjunction structure, a periodic array structure of p-type semiconductor pillar layers and n-type semiconductor pillar layers is provided in the drift layer (e.g., JP-A-2000-183350 (Kokai) and JP-A-2006-073740 (Kokai)).
In vertical power semiconductor apparatuses, high breakdown voltage is required not only in the device region where the main current path is formed during the on-time, but also in the edge termination region outside the device region.